@huningxin @wchao1115 please check these, I have some questions.
I am working on a PR to improve the steps for async and sync execution.

I noticed the following opportunities/differences:

• Inputs and their validation is the same in both, so it can be factored out and referred from both (done).
• The async steps currently are not really asynchronous. Also, they throw from a parallel job, so I assume that needs (minor) fixing (done).
• There is only one difference between the sync and async steps (excluding promise-related): the async version compares the byte length of |outputTensor| with the length of the output descriptor corresponding to |key|, whereas the sync version compares the same with the byte length of |value|. If that is deliberate, we need an editor's note on why so - please point me to relevant background there.